Golf balls having layers based on polyamide and fatty acid amide blends

ABSTRACT

Multi-piece golf balls having a solid core of at least one layer and cover of at least one layer are provided. At least one of the layers is formed from a thermoplastic polyamide composition, comprising a blend of about 40 to about 99% by weight polyamide and about 1 to about 60% by weight fatty acid amide. Preferably, the ball has a dual core construction. A rubber composition is preferably used to form the inner core and the polyamide composition is preferably used to form the outer core layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to multi-piece golf balls andmore particularly to golf balls having at least one layer made ofpolyamide/fatty acid amide compositions. The golf ball includes a corehaving at least one layer and cover having at least one layer.Preferably, the ball contains a dual-core having an inner core andsurrounding outer core layer or a multi-layered core having an innercore, intermediate core layer, and outer core layer. Preferably, atleast one of the core layers is formed from a composition comprising ablend of polyamide and fatty acid amide.

2. Brief Review of the Related Art

Multi-piece, solid golf balls are used today by recreational andprofessional golfers. Basically, these golf balls contain an inner coreprotected by a cover. The core acts as the primary engine for the balland the cover helps provide the ball with durability andwear-resistance. The core and cover may be single or multi-layered. Forexample, three-piece golf balls having an inner core, inner cover layer,and outer cover layer are popular. In other instances, golfers will usea four-piece ball containing a dual-core (inner core and surroundingouter-core layer) and dual-cover (inner cover layer and surroundingouter cover layer). Intermediate (casing) layer(s) may be disposedbetween the core and cover layers to impart various properties. Thus,five-piece and even six-piece balls can be made. Normally, the corelayers are made of a natural or synthetic rubber material or highlyneutralized ionomer polymers (HNPs). These ionomer resins are typicallycopolymers of an olefin such as ethylene; and an unsaturated carboxylicacid such as methacrylic acid, acrylic acid, or maleic acid. Metal ionssuch as sodium, lithium, zinc, and magnesium are used to neutralize theacid groups in the copolymer. The acid groups may be partially or fullyneutralized.

Such ethylene acid copolymer ionomer resins are relatively hardmaterials having good durability, cut-resistance, and toughness. Theionomers may be used to make cover, intermediate, and core layers. Whenused as a core material, the hard ionomer resin helps impart a higherinitial velocity to the golf ball. This is particularly advantageous fordriver shots off the tee. The ball tends to have good flight distance.However, one disadvantageous feature of such balls is they tend to havea hard “feel.” Some players experience a harsher, less comfortable feelwhen their club face makes contact with these hard balls. The playersenses less control and the harder ball tends to have low initial spin.It is generally more difficult to hit hard balls with the proper touchand spin. This can be particularly troublesome when making shortapproach shots with irons near the green.

Also, it is generally known that increasing the neutralization ofethylene-based ionomers reduces the processability of the material inmolding operations. Such highly neutralized ethylene-based ionomers havea decreased melt flow index. Thus, manufacturers of golf balls havelooked at making blends of ethylene-based ionomers to improve theirmelt-flow and molding properties. For example, Bulpett et al., US PatentApplication Publication 2010/0048327 discloses a golf ball having atleast one layer made from a composition comprising a highly neutralizedethylene acid copolymer and plasticizing agent selected from an innersalt, a chelate, a surfactant, a phospholipid, an ionic liquid, along-chain organic carbonate, a main-chain heteroatom-substituted fattyacid, and mixtures thereof. In particular, the carboxy-terminus of fattyacid analogs with one to three heteroatoms in the fatty acid moiety aremodified to form various amides, esters, ketones, alcohols, alcoholesters and nitrites thereof. Polar waxes such as 12-hydroxystearamide;N-(2-hydroxy ethyl) 12-hydroxystearamide; stearamide; glycerinmonostearate; sorbitan; monostearate; and 12-hydroxy stearic acid alongwith less polar waxes such as N,N′-ethylene-bis-stearamide; hydrogenatedcastor oil (castor wax), oxidized synthetic waxes, and functionalizedsynthetic waxes also may be used.

Sullivan, U.S. Pat. No. 5,120,791 discloses a golf ball comprising coreand cover, wherein the cover comprises a blend of: i) about 10 to about90 percent by weight of a hard ethylene acid copolymer ionomer (greaterthan 50 Shore D hardness and flex modulus of 15,000 to 70,000 psi); andii) i) about 10 to about 90 percent by weight of a soft ethylene acidcopolymer ionomer (20 to 40 Shore D hardness and flex modulus of 2,000to 10,000 psi). The ionomer composition may contain 0.5-1 wt. % of abis-stearamide wax to prevent clumping and mixing during processing.

In addition, it is known to add fatty acid amides to polyurethanecompositions to improve dispersability and mold processing as describedin Ichikawa et al., U.S. Pat. No. 6,833,400. In the '400 patent, adispersant selected from a fatty acid amide, montan wax, andpolyethylene wax is used, wherein the ratio of polyurethane todispersant is in the range of 100:0.2 to 100:3.0. The resultingpolyurethane composition may be used to form a golf ball cover.

Although some ionomer and polyurethane compositions may be effective formaking core layers and other components in a golf ball, there is still aneed for new compositions that can impart high quality performanceproperties to the ball. Particularly, there is a continuing need forimproved core constructions in golf balls. The core material should havegood toughness and provide the ball with high resiliency. The corematerial, however, should not be excessively hard and stiff so thatproperties such as feel, softness, and spin control are sacrificed. Thepresent invention provides golf balls having an optimum combination ofproperties.

SUMMARY OF THE INVENTION

The present invention relates to multi-piece golf balls comprising adual core having an inner core and surrounding outer core layer; and acover having at least one layer disposed about the dual core. The innercore has an outer surface and geometric center, while the outer corelayer has an outer surface and inner surface. In one preferredembodiment, the inner core comprises a rubber composition and the outercore layer consists essentially of about 40 to about 99% by weightpolyamide and about 1 to about 60% (preferably 5 to 25%) by weight fattyacid amide. In this version, the geometric center of the inner core andsurface of the outer core layer each has a hardness, and the surfacehardness of the outer core layer is greater than the center hardness ofthe inner core.

For example, the rubber composition may have a flex modulus of 1,000 to60,000 psi; and the polyamide composition may have a flex modulus of20,000 to 150,000 psi such that the flex modulus of the rubber materialis less than the flex modulus of the polyamide material. Preferably, theflex modulus of the polyamide composition is at least 15% greater thanthe flex modulus of the rubber composition. In this version, the centerhardness of the inner core is about 15 Shore D or greater, and thesurface hardness of the outer core layer is about 50 Shore D or greater.

Suitable polyamides that can be used to form the outer core layerinclude, for example, polyamide 6; polyamide 6,6; polyamide 6,10;polyamide 6,12; polyamide 11; polyamide 12; polyamide 6,9; and polyamide4,6, and copolymers and blends thereof. In one version, the fatty acidamide is a primary monoamide such as, for example, stearamide, oleamide,erucamide, behenamide, and palmitamide. In another version, substitutedmonoamides including, for example, lauryl oleamide, stearyl erucamide,hydroxy fatty acid amides, N-methylol fatty acid amides, and cocamidediethanolamide may be used. Bisamides are particularly preferred andinclude, for example, ethylene bis(stearamide) and methylenebis(oleamide). Mixtures of the foregoing fatty acid amides also may beused in the composition of this invention.

In a second preferred embodiment, the inner core consists essentially ofabout 40 to about 99% by weight polyamide and about 1 to about 60%(preferably 5 to 25%) by weight fatty acid amide; and the outer corecomprises a rubber composition. In this version, the surface hardness ofthe outer core layer is less than the center hardness of the inner core.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a three-piece golf ball having adual-core comprising an inner core/outer core, and a cover layer made inaccordance with this invention; and

FIG. 2 is a cross-sectional view of a four-piece golf ball having adual-core comprising an inner core/outer core; an inner cover layer; andan outer cover layer made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to golf balls containing atleast one component made from a thermoplastic polyamide composition. Ina particularly preferred version, a rubber composition is used to forman inner core; and a polyamide composition is used to form an outer corelayer. More particularly, the polyamide composition consists essentiallyof: i) about 40 to about 99 weight percent of polyamide; and ii) about 1to about 60 weight percent of fatty acid amide.

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three-piece, four-piece,and five-piece constructions with single or multi-layered core,intermediate, and cover portions may be made. The term, “layer” as usedherein means generally any spherical portion of the golf ball. Moreparticularly, in one version, a three-piece golf ball having a dual-coreand a cover is made. The dual-core includes an inner core (center) andsurrounding outer core layer. In another version, a four-piece golf ballcomprising a dual-core and dual-cover comprising an inner cover andouter cover is made. In yet another construction, a four-piece orfive-piece golf ball having a multi-layered core comprising an innercore (center), intermediate core layer, and outer core layer, may bemade. The golf balls of this invention may further contain anintermediate layer(s). As used herein, the term, “intermediate layer”means a layer of the ball disposed between the core and cover. Theintermediate layer also may be referred to as a casing or mantle layer.The diameter and thickness of the different layers along with propertiessuch as hardness and compression may vary depending upon theconstruction and desired playing performance properties of the golfball.

Thermoplastic Polyamides

Thermoplastic polyamides are used to form the compositions of thisinvention. The composition consists essentially of polyamide and fattyacid amide as discussed further below. The composition may contain otheringredients that do not materially affect the basic and novelcharacteristics of the composition. For example, mineral fillers may beadded to the composition as discussed further below. The composition,however, does not contain any polymers other than the polyamide. Thatis, the polyamide composition contains polyamide and fatty acid amidewith the proviso that the composition does not contain any otherpolymeric materials.

In general, polyamides refer to high molecular weight polymers in whichamide linkages (—CONH—) occur along the length of the molecular chain(Hawley's Condensed Chemical Dictionary, 13^(th) Ed.). Suitablepolyamides for use in the compositions of this invention may beobtained, for example, by: (1) polycondensation of (a) a dicarboxylicacid, such as oxalic acid, adipic acid, sebacic acid, terephthalic acid,isophthalic acid or 1,4-cyclohexanedicarboxylic acid, with (b) adiamine, such as ethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, or decamethylenediamine,1,4-cyclohexyldiamine or m-xylylenediamine; (2) a ring-openingpolymerization of cyclic lactam, such as ε-caprolactam or ω-laurolactam;(3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproicacid, 9-aminononanoic acid, 11-aminoundecanoic acid or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include, but are not limited to, nylon 6, nylon 6,6; nylon6,10; nylon 11, and nylon 12. Aliphatic and aromatic polyamides andblends thereof may be prepared in accordance with this invention.

Different commercially-available nylon resins may be used in accordancewith the present invention including, but not limited to, Trimid® andPolyram® nylon 6,6 and nylon 6 resins, available from Polymer Technology& Services, LLC; Technyl® nylon 6,6 and nylon 6 resins, available fromRhodia Engineering Plastics; Ultramid® and Capron® nylon 6 resins,available from BASF; Cristamid® and Rilsan® nylon resins, available fromArkema Inc; Vestamid® nylon resins, available from Evonik Industries;Zytel® and Elvamide® nylon resins, available from the DuPont Company;and Grivory® GTR 45 and Grilamid® TR-90, transparent nylon resins,available from Grilamid® EMS.

Different grades of polyamides and their respective properties, whichmay be used in accordance with this invention, are described in thefollowing Tables I, II, and III.

TABLE I Polyamide Resins Grade Test TRIMID TECHNYL POLYRAM PropertyMethod Units N-66 100L A205F PA100 Flexural D790 Kpsi 410 421 392Modulus Tensile ISO 527 Psi 8,700 Strength, Ultimate Tensile D 638 Psi12,000 12,300 12,300 Strength, Yield Elongation D638 % 50% 25% 4% atBreak Elongation ISO 527 %  4% at Yield Izod D256 ft lb/in 0.933 2.141.03 impact Melting D3418 ° F. 491 505 493 point *TRIMID N-66 100L is anylon 6,6 resin, available from Polymer Technology & Services, LLC.*TECHNYL A205F is a nylon 6,6 resin, available from Rhodia EngineeringPlastics. *POLYRAM PA100 is a nylon 6,6 resin, available from PolymerTechnology & Services, LLC.

TABLE II Polyamide Resins Grade Test ELVAMIDE ELVAMIDE ELVAMIDE PropertyMethod Units 8061 8063 8066 Flexural D790 Kpsi 138 131 Modulus Tensile D638 Psi 7,500 7,500 5,700 Strength Elongation D638 % 320 315 370 atbreak Izod impact D256 Melting D3418 ° F. 313 316 239 point *ELVAMIDE8061, 8063, and 8066 are nylon multi-polymer resins, available from theDuPont Company.

TABLE III Polyamide Resins Test Property Method Units ZYTEL NC010 ZYTELBK431 Flexural Modulus D790 Kpsi 247 300 Tensile Modulus ISO 527 Psi305,000 312,000 Nominal Strain at D638 % 10 14 Break Izod impact D256Melting point D3418 ° F. 581 610-625 *ZYTEL NC010 and BK431 are nylonmulti-polymer resins, available from the DuPont Company.

Polyamide homopolymers and copolymers are suitable for use in thisinvention. In general, polyamide homopolymers are produced by two commonmethods. In the first method, a compound containing one organicacid-type end group and one amine end group is formed into a cyclicmonomer. The polyamide is then formed from the monomer by a ring-openingpolymerization. These polyamides are commonly designated as nylon 6,nylon 11, nylon 12, and the like, where the number indicates the numberof carbon atoms making up the ring in the monomer. For example, nylon 6is a homopolymer of caprolactam, that is, polycaprolactam.

The second method involves the condensation polymerization of a dibasicacid and a diamine. In general, this reaction takes place as follows:

These polyamides are commonly designated as nylon 4,6; nylon 6,6; nylon6,9; nylon 6,10; nylon 6,12; and the like, where the first numberindicates the number of carbon atoms connecting the two amine groups inthe diamine and the second number indicates the number of carbon atomsconnecting the two acid groups in the dibasic acid, including those inthe acid groups. For example, nylon 6,6 is the reaction product ofhexamethylenediamine and adipic acid.

Preferred polyamide homopolymers include nylon 4, nylon 6, nylon 7,nylon 11, nylon 12, nylon 13, nylon 4,6; nylon 6,6; nylon 6,9, nylon6,10; nylon 6,12; nylon 12,12; nylon 13,13; and mixtures thereof. Morepreferred polyamide homopolymers include nylon 6, nylon 11, nylon 12,nylon 4,6; nylon 6,6; nylon 6,9; nylon 6,10; nylon 6,12; and mixturesthereof.

Compositions of nylon 6, nylon 6,6; nylon 11, and nylon 12 andcopolymers and blends thereof are particularly effective in the presentinvention. More specifically, polyamide compositions having mechanicalproperties that do not significantly change after the composition hasbeen exposed to moisture are particularly effective. These polyamidecompositions can be used to form the outer core layer and protect theinner core from moisture. The outer core layer encapsulates the innercore so that fluids do not penetrate therein. Because the polyamidecompositions are relatively stable, they are particularly effective formaking outer core layers in accordance with this invention.

As discussed above, blends of polyamides also may be used in accordancewith this invention. For example, a blend partially crystallinealiphatic polyamides and partially aromatic polyamides as disclosed inLiedloff et al., U.S. Pat. No. 7,348,046, the disclosure of which ishereby incorporated by reference, may be used. Another example of agroup of suitable polyamides is thermoplastic polyamide elastomers.Thermoplastic polyamide elastomers typically are copolymers of apolyamide and polyester or polyether. For example, the thermoplasticpolyamide elastomer can contain a polyamide (for example, nylon 6, nylon6,6; nylon 11, nylon 12 and the like) as a hard segment and a polyetheror polyester as a soft segment. In one specific example, thethermoplastic polyamides are amorphous copolyamides based on polyamide12. Compositions of polyether-amide block copolymers, which are commonlyknown as Pebax® resins and are available from Arkema, Inc. (Columbs,France), are particularly effective.

Fatty Acid Amides

The composition further contains fatty acid amides, which contain asaturated or unsaturated alkyl chain derived from a fatty acid and canbe generally classified as falling within one of the following threecategories. The first is primary monoamides having the general chemicalstructure:

wherein R is a fatty alkyl or alkenyl chain of C₈-C₂₂ and R═R″=H.Examples of primary monoamides include, but are not limited tostearamide, oleamide, erucamide, behenamide, and palmitamide

The second is substituted monoamides having the general chemicalstructure:

These substituted monoamides include secondary, tertiary, andalkanolamides, wherein R is a fatty alkyl or alkenyl chain of C₅-C₂₃;and R′ and R″ may be a hydrogen, fatty alkyl, alkenyl, aryl, or alkyleneoxide condensation groups with at least one alkyl, alkenyl, aryl, oralkylene oxide group. Examples of substituted monoamides include, butare not limited to, lauryl oleamide, stearyl erucamide, hydroxy fattyacid amides, N-methylol fatty acid amides, and cocamide diethanolamide.

The third category is bisamides having the general chemical structure:

wherein, the R groups are fatty alkyl or alkenyl chains. R* is amethylene or ethylene group, and R′ and R″ may be hydrogen, fatty alkyl,alkylene, aryl, or alkylene oxide condensation groups. Examples ofsuitable bisamides include, but are not limited, to ethylenebis(stearamide) and methylene bis(oleamide). R could also be a hydroxyfatty acid in any of the above three categories.

Many polyamides are semi-crystalline thermoplastic polymers containingamorphous and crystalline regions. The amorphous regions contributeelasticity and the crystalline regions contribute strength and rigidityto the polymer. The polar amide groups in the backbone chains of thepolyamide polymer are attracted to each other. These groups form stronghydrogen bonds between the chains, thus providing a crystalline network.In other instances, the polyamides have a fully amorphous or crystallinenature. It is also recognized that blends of amorphous polyamides andsemi-crystalline polyamides may be prepared and used in accordance withthis invention. For example, such amorphous/semi-crystalline polyamideblends, which may further contain toughening agents as disclosed inEpstein et al., U.S. Pat. No. 4,410,661, the disclosure of which ishereby incorporated by reference, may be used.

While not wishing to be bound by any theory, it is believed that addingthe fatty acid amide may disrupt the polyamide chains. Particularly, thefatty acid amide may be added in a sufficient amount so that itpartially reduces the crystallinity of the polyamide. Preferably, thecrystallinity of the polyamide is reduced by at least 1%. That is, thefirst polyamide (containing polyamide only) composition has a firstpercentage of crystallinity and the second polyamide (containingpolyamide and fatty acid salt) composition has a second percentage ofcrystallinity. In a preferred embodiment, the second crystallinitypercent value is at least 1% less; or at least 2% less; or at least 4%less; or at least 8% less; or at least 10% less than the firstcrystallinity percent value. The crystallinity of the polyamide may bedetermined by conventional techniques such as differential scanningcalorimetry which measures the amount of heat absorbed or released bythe sample as the sample undergoes a physical transformation.Determining the crystallinity of polyamide 6 and polyamide 6,6 isparticularly effective and such polyamides can be used in accordancewith this invention. By partially reducing the crystallinity of thepolyamide, it becomes softer and more rubbery. Since the polyamide isless hard and stiff, it can be used to form the outer core layer andhelp impart a softer compression to the core. The compression of thedual-core (inner core (center) and surrounding outer core layer) ispreferably within the range of about 30 to about 110, more preferablywithin the range of about 50 to about 100, and even more preferablywithin the range of about 70 to about 90.

It is believed that the fatty acid amide should be added in a sufficientamount to the polyamide composition so that there is a substantialchange in the crystallinity of the polyamide polymer. Thus, although theconcentration of fatty acid salt may be as little as 1% by weight toform some polyamide compositions per this invention, it is preferredthat the concentration of fatty acid salt be at least 5 wt. %, morepreferably at least 8 wt. %, and even more preferably at least 11 wt. %based on total weight of the composition. More particularly, it ispreferred that the fatty acid salt be present in an amount within arange having a lower limit of 5% or 8% or 11% or 15% or 18% or 20% andan upper limit of 22% or 25% or 30% or 40% or 50% or 60%. In onepreferred embodiment, the concentration of fatty acid amide falls withinthe range of about 5% to about 25%. In the present invention, it ispreferred that the fatty acid amide be present at a relatively highconcentration to cause the crystallinity of the polyamide polymer tochange substantially. This helps impart some advantageous properties tothe composition making it particularly effective for use in a golf ball.

Flex Modulus and Hardness of Composition

As discussed above, in one preferred version, the thermoplasticpolyamide composition is used to form an outer core and a rubbercomposition is used to form an inner core. In one embodiment, thepolyamide composition is relatively stiff and the rubber composition isrelatively flexible. That is, in one embodiment, the flex modulus andhardness of the polyamide material is greater than the flex modulus andhardness of the rubber material.

More particularly, in one embodiment, the polyamide composition has aflex modulus lower limit of 20,000 or 30,000 or 40,000 or 50,000 or60,000 or 70,000 or 80,000 or 90,000 or 100,000; and a flex modulusupper limit of 110,000 or 120,000 or 130,000 psi or 140,000 or 160,000or 180,000 or 200,000 or 300,000 or 400,000 or 500,000 psi or greater.In general, the properties of flex modulus and hardness are related,whereby flex modulus measures the material's resistance to bending andhardness measures the material's resistance to indentation. In general,as the flex modulus of the material increases, the hardness of thematerial also increases. Thus, in one embodiment, the polyamidecomposition is relatively hard having a hardness of 40 Shore D orgreater, or 50 Shore D or greater, or 60 Shore D or greater, or within arange having a lower limit of 40 or 50 or 60 Shore D and an upper limitof 80 or 90 or 100 Shore D.

It is believed that adding the fatty acid amide to the polyamide helpsmake the composition softer and more rubbery (although thepolyamide/fatty acid amide composition is still considered relativelystiff versus the rubber composition as discussed above.) Thus, in oneembodiment, the first polyamide (containing polyamide only) compositionhas a first flex modulus value and the second polyamide (containingpolyamide and fatty acid amide) composition has a second flex modulusvalue, wherein the second flex modulus value is at least 1% less; or atleast 2% less; or at least 4% less; or at least 8% less; or at least 10%less than the first modulus value.

Conversely, in one preferred version, the rubber composition isrelatively flexible. More particularly, in one embodiment, the rubbercomposition has a flex modulus lower limit of 1,000 or 5,000 or 10,000or 15,000 or 20,000 or 25,000 or 30,000 psi and an upper limit of 40,000or 45,000 or 50,000 or 60,000 or 70,000 or 80,000 psi. As discussedabove, the hardness and flex modulus of the material are generallyrelated and as the hardness of the material decreases, the flex modulusof the material also decreases. Thus, in one embodiment, the rubbercomposition has a hardness of 30 Shore D or less; or 40 Shore D or less;or 50 Shore D or less; or 60 Shore D or less. In another embodiment, thehardness of the rubber composition falls within a range having a lowerlimit of 15 or 30 or 40 or 50 Shore D and an upper limit of 60 or 70 or80 or 85 Shore D.

Test methods for measuring the flex modulus and hardness of thematerials are described further below. In some instances, it may be morefeasible to measure the hardness of the golf ball layer (that is,“hardness on the ball”), and this test method also is described below.

By the term, “modulus” as used herein, it is meant flexural moduluswhich is the ratio of stress to strain within the elastic limit (whenmeasured in the flexural mode) and is similar to tensile modulus. Thisproperty is used to indicate the bending stiffness of a material. Theflexural modulus, which is a modulus of elasticity, is determined bycalculating the slope of the linear portion of the stress-strain curveduring the bending test. The formula used to calculate the flexuralmodulus from the recorded load (F) and deflection (D) is:

$E_{B} = {\frac{3}{4}\frac{{FL}^{3}}{{bd}^{3}D}}$

wherein,

L=span of specimen between supports (m);

b=width (m); and

d=thickness (m)

If the slope of the stress-strain curve is relatively steep, thematerial has a relatively high flexural modulus meaning the materialresists deformation. The material is more rigid. If the slope isrelatively flat, the material has a relatively low flexural modulusmeaning the material is more easily deformed. The material is moreflexible. Flexural modulus can be determined in accordance with ASTMD790 standard among other testing procedures.

Additives and Fillers

A wide variety of non-polymeric additives and fillers may be included inthe final polyamide composition. Suitable additives and mineral fillersinclude, for example, precipitated hydrated silica, clay, talc,asbestos, glass fibers, aramid fibers, mica, calcium metasilicate,barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide,diatomaceous earth, polyvinyl chloride, carbonates such as calciumcarbonate and magnesium carbonate. Suitable metal fillers includetitanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, lead,copper, boron, cobalt, beryllium, zinc, and tin. Suitable metal alloysinclude steel, brass, bronze, boron carbide whiskers, and tungstencarbide whiskers. Suitable metal oxide fillers include zinc oxide, ironoxide, aluminum oxide, titanium dioxide, magnesium oxide, and zirconiumoxide. Suitable particulate carbonaceous fillers include graphite,carbon black, cotton flock, natural bitumen, cellulose flock, andleather fiber. Micro balloon fillers such as glass and ceramic, and flyash fillers can also be used.

Other additives and fillers include, but are not limited to, chemicalblowing and foaming agents, optical brighteners, coloring agents,fluorescent agents, whitening agents, ultraviolet (UV) light absorbers,UV light stabilizers, defoaming agents, processing aids, antioxidants,stabilizers, softening agents, fragrance components, plasticizers, andimpact modifiers. In a particular embodiment, the total amount ofadditive(s) and filler(s) present in the polyamide composition is 25 wt.% or less; or 20 wt. % or less; or 15 wt. % or less; or 12 wt. % orless, or 10 wt. % or less; or 9 wt. % or less; or 6 wt. % or less; or 5wt. % or less; or 4 wt. % or less; or 3 wt. % or less, based on thetotal weight of the polyamide composition. More particularly, thepolyamide composition may include filler(s) selected from carbon black,nanoclays (e.g., Cloisite® and Nanofil® nanoclays, commerciallyavailable from Southern Clay Products, Inc., and Nanomax® and Nanomer®nanoclays, commercially available from Nanocor, Inc.), talc (e.g.,Luzenac HAR® high aspect ratio talcs, commercially available fromLuzenac America, Inc.), glass (e.g., glass flake, milled glass, andmicroglass), mica and mica-based pigments (e.g., Iriodin® pearl lusterpigments, commercially available from The Merck Group), and combinationsthereof. Organic fiber micropulp also may be added. Polyamide-claynanocomposites such as an amorphous polyamide resin containing a claymaterial uniformly dispersed therein, as disclosed in Lan et al., U.S.Pat. No. 6,376,591 also may be used in the polyamide composition.

In another version, the polyamide compositions may contain carbon fibersor carbon fiber sheets comprising a weave of thin carbon fibers heldtogether in a resin. In yet another version, the polyamide compositionsmay contain forged composite material composed of bundles of microscopiccarbon fibers held together in a resin. These turbostratic carbon fibersare randomly dispersed in the resin. The structure of the forgedcomposite material differs over traditional carbon fiber sheets. Theforged composite material contains discontinuous fibers intertwined inthe resin; while ordinary carbon fiber sheets are woven—they contain aweave of fibers. As a result, the forged composite material is verylightweight and has high mechanical strength.

In accordance with the present invention, golf balls containingdual-cores formed from the thermoplastic polyamide composition haveseveral advantageous properties. For example, the dual-core helpsprovide the golf ball with good resiliency (distance) withoutsacrificing a nice feel to the ball. As discussed above, some polyamidesmay have a relatively high flex modulus and golf ball layers made fromsuch a polyamide, by and in itself, can be overly stiff and brittle. Ifthis layer is too stiff, the golf ball may have a hard “feel.” Now, inaccordance with the present invention, it has been found that polyamidecompositions consisting essentially of polyamide and fatty acid amidecan be used to form a golf ball layer having an optimum combination ofproperties. Particularly, the polyamide composition may be used as acore material. The resulting ball has a relatively high coefficient ofrestitution (COR) allowing it to reach high velocity when struck by agolf club. Thus, the ball tends to travel a greater distance which isparticularly important for driver shots off the tee. At the same time,the compositions are not excessively hard and they help impart a softand comfortable feel to the ball. The player experiences a better senseof control and natural feeling when making the shot. Meanwhile, thecompression of the dual-core (inner core (center) and surrounding outercore layer) is preferably within the range of about 30 to about 110,more preferably within the range of about 50 to about 100, and even morepreferably within the range of about 70 to about 90.

Core Structure

As discussed above, the core is preferably a dual-core comprising aninner core (center) made from a rubber composition and a surroundingouter core layer made from a thermoplastic polyamide composition.

Any suitable rubber compositions known in the art may be used to makethe inner core (center) of the ball in accordance with this invention.In general, such rubber compositions contain a base rubber, free-radicalinitiators, crosslinking agents, and filler. Suitable base rubbersinclude, for example, polybutadiene, ethylene-propylene rubber,ethylene-propylene-diene rubber, polyisoprene, styrene-butadiene rubber,polyalkenamers, butyl rubber, halobutyl rubber, or polystyreneelastomers.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; DIENE 55NF, 70AC, and 320 AC, available fromFirestone Polymers of Akron, Ohio; and PBR-Nd Group II and Group III,available from Nizhnekamskneftekhim, Inc. of Nizhnekamsk, TartarstanRepublic.

The rubber compositions of this invention may be cured, either bypre-blending or post-blending, using conventional curing processes.Suitable curing processes include, for example, peroxide-curing,sulfur-curing, high-energy radiation, and combinations thereof.Preferably, the rubber composition contains a free-radical initiatorselected from organic peroxides, high energy radiation sources capableof generating free-radicals, and combinations thereof. In one preferredversion, the rubber composition is peroxide-cured. Suitable organicperoxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel.

Radical scavengers such as a halogenated organosulfur or metal saltthereof, organic disulfide, or inorganic disulfide compounds may beadded to the rubber composition. These compounds also may function as“soft and fast agents.” As used herein, “soft and fast agent” means anycompound or a blend thereof that is capable of making a core: 1) softer(having a lower compression) at a constant “coefficient of restitution”(COR); and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

The rubber compositions of the present invention also may includefillers, which are added to adjust the density and/or specific gravityof the material. Suitable fillers include, but are not limited to,polymeric or mineral fillers, metal fillers, metal alloy fillers, metaloxide fillers and carbonaceous fillers. The fillers can be in anysuitable form including, but not limited to, flakes, fibers, whiskers,fibrils, plates, particles, and powders. Rubber regrind, which isground, recycled rubber material (for example, ground to about 30 meshparticle size) obtained from discarded rubber golf ball cores, also canbe used as a filler. The amount and type of fillers utilized aregoverned by the amount and weight of other ingredients in the golf ball,since a maximum golf ball weight of 45.93 g (1.62 ounces) has beenestablished by the United States Golf Association (USGA).

Preferably, the base rubber material is polybutadiene rubber, and thismaterial may be blended with other elastomers in accordance with thisinvention. Other elastomers include, but are not limited to,polybutadiene, polyisoprene, ethylene propylene rubber (“EPR”),styrene-butadiene rubber, styrenic block copolymer rubbers (such as“SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene,“I” is isobutylene, and “B” is butadiene), polyalkenamers such as, forexample, polyoctenamer, butyl rubber, halobutyl rubber, polystyreneelastomers, polyethylene elastomers, polyurethane elastomers, polyureaelastomers, metallocene-catalyzed elastomers and plastomers, copolymersof isobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and combinations of two ormore thereof.

The rubber compositions also preferably include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA).

In one version, the surface hardness of the outer core layer (polyamidecomposition) is greater than the center hardness of the inner core(rubber composition). Preferably, the inner core has a center hardness(CH) within a range having a lower limit of 15 or 25 or 30 or 35 or 40or 45 or 50 or 55 Shore D and an upper limit of 60 or 65 or 70 or 75 or80 or 85 or 90 Shore D. The inner core (center) also preferably has asurface hardness (ICSH) within a range having a lower limit of 15 or 20or 30 or 35 or 40 or 45 or 50 or 55 Shore D and an upper limit of 60 or65 or 70 or 75 or 80 or 85 or 90 Shore D. Meanwhile, the outer corelayer preferably has a surface hardness (OCLSH) within a range having alower limit of 40 or 45 or 50 or 55 Shore D and an upper limit of 60 or65 or 70 or 75 or 80 or 85 or 90 Shore D. In an alternative version, thepolyamide composition is used to form the inner core, while the rubbercomposition is used to form the outer core; and preferably the centerhardness of the inner core (polyamide) is greater than the surfacehardness of the outer core layer (rubber).

Particularly, in one preferred instance, the center hardness of theinner core is in the range of about 30 to about 82 Shore D units and thesurface hardness of the outer core is in the range of about 40 to about87 Shore D units. More particularly, the center hardness of the innercore is about 15 Shore D units or greater and the surface hardness ofthe outer core is about 50 Shore D units or greater. In these instances,the surface hardness (outer core) is preferably at least 5 Shore D unitsgreater than the center hardness (inner core).

As discussed above, in another instance, the center hardness of theinner core is greater than the surface hardness of the outer core layer.For example, the center hardness may be about 40 Shore D units orgreater and the surface hardness of the outer core may be about 30 ShoreD units or greater. In these instances, the center hardness (inner core)is preferably at least 5 Shore D units greater than the surface hardness(outer core).

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center) and the outer core layer has a“positive” hardness gradient (that is, the outer surface of the outercore layer is harder than the inner surface of the outer core layer.) Incases where both the inner core and outer core layer have “positive”hardness gradients, the outer surface hardness of the outer core layeris still preferably greater than the material hardness of the inner core(center).

In another version, the inner core (center) has a positive hardnessgradient, while the outer core layer has a “negative” hardness gradient(that is, the outer surface of the outer core layer is softer than theinner surface of the outer core layer.) In yet another version, theouter core layer may have a “zero” hardness gradient. (That is, thehardness values of the outer surface of the outer core layer and theinner surface of the outer core layer are substantially the same.)Particularly, the term, “zero hardness gradient” as used herein, means asurface to center (or second surface) Shore C hardness gradient of lessthan 8, preferably less than 5 and most preferably less than 3 and mayhave a value of zero or negative 1 to negative 25. The term, “negativehardness gradient” as used herein, means a surface to center (or secondsurface) Shore C hardness gradient of less than zero. The terms, “zerohardness gradient” and “negative hardness gradient,” may be used hereininterchangeably to refer to hardness gradients of negative 1 to negative25. The term, “positive hardness gradient” as used herein, means asurface to center (or second surface) Shore C hardness gradient of 8 orgreater, preferably 10 or greater, and most preferably 20 or greater. Bythe term, “steep positive hardness gradient” as used herein, it is meantsurface to center (or second surface) Shore C hardness gradient of 20 orgreater, more preferably 25 or greater, and most preferably 30 orgreater. For example, the core may have a steep positive hardnessgradient of 35, 40, or 45 Shore C or greater.

In one particular version, the hardness gradient from the geometriccenter of the inner core to the surface of the outer core layer is apositive hardness gradient. That is, the outer surface of the outer corelayer is harder than the center of the inner core. Methods for measuringthe hardness of the core and cover layers and determining the hardnessgradients are discussed in further detail below.

As discussed above, the dual-core constitutes an inner core (center) andan outer core layer. The inner core preferably has a diameter within arange having a lower limit of 0.125 or 0.130 or 0.140 or 0.150 or 0.20or 0.40 or 0.80 inches and an upper limit of 1.125 or 1.20 or 1.40 or1.50 or 1.55 inches. More preferably, the inner core has a diameter inthe range of about 0.125 to about 1.50 inches. The outer core preferablyhas a thickness within a range having a lower limit of 0.010 or 0.020 or0.025 or 0.030 or 0.035 or 0.040 inches and an upper limit of 0.070 or0.080 or 0.090 or 0.100 or 0.120 or 0.140 or 0.300 or 0.400 or 0.500 or0.600 or 0.700 inches. Particularly, the outer core layer may have athickness in the range of about 0.010 to about 0.570 inches and morepreferably in the range of about 0.020 to about 0.280 inches. In otherembodiments, particularly when the polyamide composition is used to formthe inner core, the inner core may be smaller. For example, the innercore may have a diameter in the range of about 0.050 to about 1.40inches, more preferably about 0.100 to about 0.700 inches. In suchcases, the outer core layer may have a thickness in the range of about0.020 to about 0.650 inches. The outer core layer encloses the innercore such that the two-layered core has an overall diameter within arange having a lower limit of 1.20 or 1.30 or 1.40 or 1.50 or 1.51 or1.52 or 1.525 inches and an upper limit of 1.54 or 1.55 or 1.555 or 1.56or 1.59 or 1.62 or 1.64 inches.

Cover Structure

The golf ball cores of this invention may be enclosed with one or morecover layers. In addition, as discussed above, an intermediate layer maybe disposed between the core and cover layers. The intermediate layerpreferably has good moisture vapor barrier properties to preventmoisture from penetrating into the core structure. The cover layerspreferably have good impact durability and scuff-resistance. Thepolyamide compositions of this invention may be used to form at leastone of the intermediate and/or cover layers. In other versions, theintermediate layer and cover layers are formed from other polymericmaterials.

For example, the intermediate and cover layers may be formed from a widevariety of materials including, for example, polyurethanes; polyureas;copolymers, blends and hybrids of polyurethane and polyurea; ethyleneacid copolymer ionomer resins (for example, Surlyn® ionomer resins andHPF® 1000 and HPF® 2000, commercially available from DuPont; Iotek®ionomers, commercially available from ExxonMobil Chemical Company;Amplify® JO ionomers of ethylene acrylic acid copolymers, commerciallyavailable from The Dow Chemical Company; and Clarix® ionomer resins,commercially available from A. Schulman Inc.); polyethylene, including,for example, low density polyethylene, linear low density polyethylene,and high density polyethylene; polypropylene; rubber-toughened olefinpolymers; acid copolymers, for example, poly(meth)acrylic acid, which donot become part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to help make a golf ballhaving high resiliency and a soft feel. By the term, “hybrids ofpolyurethane and polyurea,” it is meant to include copolymers and blendsof polyurethanes and polyureas.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

In one preferred embodiment, the ball includes a dual-cover comprisinginner and outer cover layers. The inner cover layer is preferably formedfrom a composition comprising an ionomer or a blend of two or moreionomers that helps impart hardness to the ball. The inner cover layerpreferably has a material hardness of 95 Shore C or less, or less than95 Shore C, or 92 Shore C or less, or 90 Shore C or less, or a materialhardness within a range having a lower limit of 60 or 65 or 70 or 75 or80 or 84 or 85 Shore C and an upper limit of 90 or 92 or 95 Shore C. Thethickness of the inner cover layer is preferably within a range having alower limit of 0.010 or 0.015 or 0.020 or 0.030 inches and an upperlimit of 0.035 or 0.045 or 0.080 or 0.120 inches. The outer cover layerpreferably has a material hardness of 85 Shore C or less. The thicknessof the outer cover layer is preferably within a range having a lowerlimit of 0.010 or 0.015 or 0.025 inches and an upper limit of 0.035 or0.040 or 0.055 or 0.080 inches.

In a particular embodiment, the inner cover layer is formed from acomposition comprising a high acid ionomer. A particularly suitable highacid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is a copolymer ofethylene and methacrylic acid, having an acid content of 19 wt %, whichis 45% neutralized with sodium. In another particular embodiment, theinner cover layer is formed from a composition comprising a high acidionomer and a maleic anhydride-grafted non-ionomeric polymer. Aparticularly suitable maleic anhydride-grafted polymer is Fusabond 525D®(DuPont), which is a maleic anhydride-grafted, metallocene-catalyzedethylene-butene copolymer having about 0.9 wt % maleic anhydride graftedonto the copolymer. One example of a blend of high acid ionomer andmaleic anhydride-grafted polymer is 84 wt. %/16 wt. % blend of Surlyn8150® and Fusabond 525D®. Blends of high acid ionomers with maleicanhydride-grafted polymers are further disclosed, for example, in U.S.Pat. Nos. 6,992,135 and 6,677,401, the entire disclosures of which arehereby incorporated herein by reference.

In another embodiment, the inner cover layer is formed from acomposition comprising a 50/45/5 blend of Surlyn® 8940/Surlyn®9650/Nucrel® 960, and, in a particularly preferred embodiment, has amaterial hardness of from 80 to 85 Shore C. In another particularembodiment, the inner cover layer is formed from a compositioncomprising a 50/25/25 blend of Surlyn® 8940/Surlyn® 9650/Surlyn® 9910,preferably having a material hardness of about 90 Shore C. In onepreferred version, a blend of 50% Surlyn® 7940 and 50% Surlyn® 8940 isused to form the inner cover. In yet another particular embodiment, theinner cover layer is preferably formed from a composition comprising a50/50 blend of Surlyn® 8940/Surlyn® 9650, preferably having a materialhardness of about 86 Shore C. Surlyn® 8940 is an ethylene/methacrylicacid copolymer in which the MAA acid groups have been partiallyneutralized with sodium ions. Surlyn® 9650 and Surlyn® 9910 are twodifferent grades of ethylene/methacrylic acid copolymer in which the MAAacid groups have been partially neutralized with zinc ions. Surlyn® 7940is a copolymer of about 85% ethylene and 15% methacrylic acid that hasbeen neutralized with lithium ions. Nucrel® 960 is anethylene/methacrylic acid copolymer resin nominally made with 15 wt %methacrylic acid, and available from DuPont.

As discussed above, the dual-core of the golf ball may be enclosed witha single-layered or multi-layered covers. In one embodiment, asingle-layered cover having a thickness in the range of about 0.015 toabout 0.090 inches, more preferably about 0.030 to about 0.070 inches,is formed. The cover has a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. In anotherembodiment, a multi-layered cover comprising inner and outer coverlayers is formed, where the inner cover layer preferably has a thicknessof about 0.011 inches to about 0.110 inches, more preferably about 0.02inches to about 0.08 inches. In this version, the inner cover layer isformed from a blend of partially- or fully-neutralized ionomers, and thecover has a Shore D hardness of greater than about 55, more preferablygreater than about 60, and most preferably greater than about 65. Theouter cover layer, in this embodiment, preferably has a thickness ofabout 0.010 inches to about 0.100 inches, more preferably about 0.02inches to about 0.06 inches, and most preferably about 0.025 inches toabout 0.045 inches, with a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. Thus, thecover may comprise two or more layers and preferably has an overallthickness of about 0.020 to about 0.160 inches. The inner cover layer isharder than the outer cover layer in this version. A preferred outercover layer is a castable or reaction injection molded polyurethane,polyurea or copolymer, blend, or hybrid thereof having a Shore Dhardness of about 40 to about 50. In another multi-layer cover,dual-core embodiment, the outer cover and inner cover layer materialsand thickness are the same but, the hardness range is reversed; that is,the outer cover layer is harder than the inner cover layer.

Golf Ball Constructions

As discussed above, the thermoplastic polyamide compositions of thisinvention may be used to form a core for any suitable ball construction,including, for example, three-piece, four-piece, and five-piece designs.

The solid cores for the golf balls of this invention may be made usingany suitable conventional technique such as, for example, compression orinjection molding. Typically, the inner core is formed by compressionmolding a slug of uncured or lightly cured rubber material into aspherical structure. The outer core, which surrounds the inner core, isformed by molding the polyamide composition over the inner core.Compression or injection molding techniques may be used. Then, theintermediate and/or cover layers are applied. Prior to this step, thecore structure may be surface-treated to increase the adhesion betweenits outer surface and the next layer that will be applied over the core.Such surface-treatment may include mechanically or chemically-abradingthe outer surface of the core. For example, the core may be subjected tocorona-discharge, plasma-treatment, silane-dipping, or other treatmentmethods known to those in the art.

The cover layers are formed over the core or ball subassembly (the corestructure and any intermediate layers disposed about the core) using asuitable technique such as, for example, compression-molding,flip-molding, injection-molding, retractable pin injection-molding,reaction injection-molding (RIM), liquid injection-molding, casting,spraying, powder-coating, vacuum-forming, flow-coating, dipping,spin-coating, and the like. Preferably, each cover layer is separatelyformed over the ball subassembly. For example, an ethylene acidcopolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the ball subassembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the subassembly. Inanother method, the ionomer composition is injection-molded directlyonto the core using retractable pin injection molding. An outer coverlayer comprising a polyurethane composition may be formed by using acasting process.

For example, in one version of the casting process, a liquid mixture ofreactive polyurethane prepolymer and chain-extender (curing agent) ispoured lower and upper mold cavities. Then, the golf ball subassembly islowered at a controlled speed into the reactive mixture. Ball suctioncups can hold the ball subassembly in place via reduced pressure orpartial vacuum. After sufficient gelling of the reactive mixture(typically about 4 to about 12 seconds), the vacuum is removed and theintermediate ball is released into the mold cavity. Then, the upper moldcavity is mated with the lower mold cavity under sufficient pressure andheat. An exothermic reaction occurs when the polyurethane prepolymer andchain extender are mixed and this continues until the cover materialencapsulates and solidifies around the ball subassembly. Finally, themolded balls are cooled in the mold and removed when the molded cover ishard enough so that it can be handled without deformation.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball.

Referring to FIG. 1, one version of a golf ball that can be made inaccordance with this invention is generally indicated at (8). The ball(8) contains a dual-core (10) having an inner core (center) (10 a) andouter core layer (10 b) surrounded by a single-layered cover (12). Thecenter (10 a) is formed preferably from a rubber composition asdiscussed above. The outer core layer (10 b) is formed from a polyamidecomposition as discussed above. In FIG. 2, a golf ball (15) containingthe above-described dual-core (10) is surrounded by a dual-cover (18)having an inner cover layer (18 a) and outer cover layer (18 b), whichmay be formed from any of the cover materials described above.

The surfaces of the golf balls shown in FIGS. 1-2 may have variousdimple patterns to modify the aerodynamic properties of the ball. Itshould be understood the golf balls shown in FIGS. 1-2 are forillustrative purposes only and not meant to be restrictive. Other golfball constructions can be made in accordance with this invention.

For example, a golf ball containing an inner core (center); anintermediate core layer; and an outer core layer may be made. The centerpreferably has a diameter within a range having a lower limit of 0.100or 0.125 or 0.250 inches and an upper limit of 0.375 or 0.500 or 0.750or 1.00 or 1.30 inches. The intermediate core layer preferably has athickness within a range having a lower limit of 0.050 or 0.100 or 0.150or 0.200 inches and an upper limit of 0.300 or 0.350 or 0.400 or 0.500inches. The outer core layer encloses the center and intermediate corelayer structure such that the multi-layer core has an overall diameterwithin a range having a lower limit of 1.40 or 1.45 or 1.50 or 1.55inches and an upper limit of 1.58 or 1.60 or 1.62 or 1.66 inches.

In one embodiment, the inner core (center) is made of the polyamidecomposition of this invention. The surrounding intermediate core layeris made of a rubber composition comprising a base rubber such as, forexample, polybutadiene, polyisoprene, ethylene propylene rubber (EPR),ethylene propylene diene rubber (EPDM), styrene-butadiene rubber,styrenic block copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”,“SIBS”, and the like, where “S” is styrene, “I” is isobutylene, and “B”is butadiene), polyalkenamers such as, for example, polyoctenamer, butylrubber, halobutyl rubber, and polystyrene elastomers. Finally, the outercore layer also is made of the polyamide composition of this invention.

In the above-described version, the center and outer core layers(polyamide compositions) preferably each has an outer surface hardnessof 40 Shore D or greater, more preferably a surface hardness of 60 ShoreC or greater, and most preferably a surface hardness of 70 Shore C orgreater. For example, the center may have an outer surface hardnesswithin a range having a lower limit of 45 or 55 or 65 Shore D and anupper limit of 75 or 85 or 95 Shore D. Meanwhile, the intermediate corelayer (rubber composition) may have an outer surface hardness that isless than that of the center and is preferably 50 Shore C or less; or 60Shore C or less; or 70 Shore C or less; or 75 Shore C or less; or 80Shore C or less.

It is recognized that additional golf ball constructions can be madewithout departing from the spirit and scope of the present invention.For example, in another version, a golf ball containing a multi-layeredcore having: i) an inner core (center) made of a rubber composition asdescribed above; ii) a surrounding intermediate core layer made of thepolyamide composition of this invention; and iii) an outer core layermade of a rubber composition, can be manufactured. In yet anotherversion, both the inner core (center) and intermediate core layer eachare made of a rubber composition; and the outer core layer is made ofthe polyamide composition of this invention. In a further embodiment,both the inner core (center) and intermediate core layer are made of thepolyamide composition of this invention; and the outer core layer ismade of a rubber composition.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball subassembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dhardness) was measured according to the test method ASTM D-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, “compression” refers to Atti compression and is measuredaccording to a known procedure, using an Atti compression test device,wherein a piston is used to compress a ball against a spring. The travelof the piston is fixed and the deflection of the spring is measured. Themeasurement of the deflection of the spring does not begin with itscontact with the ball; rather, there is an offset of approximately thefirst 1.25 mm (0.05 inches) of the spring's deflection. Very lowstiffness cores will not cause the spring to deflect by more than 1.25mm and therefore have a zero compression measurement. The Atticompression tester is designed to measure objects having a diameter of42.7 mm (1.68 inches); thus, smaller objects, such as golf ball cores,must be shimmed to a total height of 42.7 mm to obtain an accuratereading. Conversion from Atti compression to Riehle (cores), Riehle(balls), 100 kg deflection, 130-10 kg deflection or effective moduluscan be carried out according to the formulas given in J. Dalton.Compression may be measured as described in McNamara et al., U.S. Pat.No. 7,777,871, the disclosure of which is hereby incorporated byreference.

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball subassembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

When numerical lower limits and numerical upper limits are set forthherein, it is contemplated that any combination of these values may beused. Other than in the operating examples, or unless otherwiseexpressly specified, all of the numerical ranges, amounts, values andpercentages such as those for amounts of materials and others in thespecification may be read as if prefaced by the word “about” even thoughthe term “about” may not expressly appear with the value, amount orrange. Accordingly, unless indicated to the contrary, the numericalparameters set forth in the specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the present invention.

All patents, publications, test procedures, and other references citedherein, including priority documents, are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted.

It is understood that the compositions and golf ball products describedand illustrated herein represent only some embodiments of the invention.It is appreciated by those skilled in the art that various changes andadditions can be made to compositions and products without departingfrom the spirit and scope of this invention. It is intended that allsuch embodiments be covered by the appended claims.

We claim:
 1. A golf ball, comprising: a) a dual core comprising an innercore and outer core layer, the inner core having an outer surface andgeometric center and the outer core layer having an outer surface andinner surface; the inner core comprising a rubber composition and theouter core consisting essentially of about 40 to about 99% by weightpolyamide and about 1 to about 60% by weight fatty acid amide, whereinthe center of the inner core and surface of the outer core layer eachhas a hardness, and the surface hardness of the outer core layer isgreater than the center hardness of the inner core; and b) a coverhaving at least one layer disposed about the core.
 2. The golf ball ofclaim 1, wherein the polyamide is selected from the group consisting ofpolyamide 6; polyamide 6,6; polyamide 6,10; polyamide 6,12; polyamide11; polyamide 12; polyamide 6,9; and polyamide 4,6, and copolymers andblends thereof.
 3. The golf ball of claim 1, wherein the fatty acidamide is a primary monoamide selected from the group consisting ofstearamide, oleamide, erucamide, behenamide, and palmitamide, andmixtures thereof.
 4. The golf ball of claim 3, wherein the primarymonoamide is a substituted monoamide selected from the group consistingof lauryl oleamide, stearyl erucamide, hydroxy fatty acid amides,N-methylol fatty acid amides, and cocamide diethanolamide, and mixturesthereof.
 5. The golf ball of claim 1, wherein the fatty acid amide is abisamide selected from the group consisting of ethylene bis(stearamide),methylene bis(oleamide), and mixtures thereof.
 6. The golf ball of claim1, wherein the rubber composition has a flex modulus of 1,000 to 60,000psi and the polyamide composition is relatively stiff has a flex modulusof 20,000 psi to 150,000 psi, the flex modulus of the rubber compositionbeing less than the flex modulus of the polyamide composition.
 7. Thegolf ball of claim 6, wherein the modulus of the polyamide compositionis at least 15% greater than the modulus of the rubber composition. 8.The golf ball of claim 6, wherein the center hardness of the inner coreis about 15 Shore D or greater and the surface hardness of the outercore is about 50 Shore D or greater, the center hardness of the innercore being less than the surface hardness of the outer core layer. 9.The golf ball of claim 1, wherein the inner core has a diameter in therange of about 0.125 to about 1.50 inches.
 10. The golf ball of claim 1,wherein the outer core layer has a thickness in the range of about 0.020to about 0.280 inches.
 11. The golf ball of claim 1, wherein thedual-core core has an overall compression in the range of about 40 toabout
 110. 12. The golf ball of claim 11, wherein the dual-core has anoverall compression in the range of about 70 to about
 100. 13. The golfball of claim 1, wherein the cover is a single layer having a thicknessof about 0.015 to about 0.090 inches and is formed from a thermoplasticor thermoset material.
 14. The golf ball of claim 1, wherein the covercomprises two or more layers and has an overall thickness of about 0.020to about 0.160 inches and wherein each cover layer is formed from athermoplastic or thermoset material.
 15. A golf ball, comprising: a) adual core having an inner core and outer core layer, the inner corehaving an outer surface and geometric center and the outer core layerhaving an outer surface and inner surface; the inner core consistingessentially of about 40 to about 99% by weight polyamide and about 1 toabout 60% by weight fatty acid amide and the outer core layer comprisinga rubber composition, wherein the center of the inner core and surfaceof the outer core layer each has a hardness and the center hardness ofthe inner core is greater than the surface hardness of the outer corelayer; and b) a cover having at least one layer disposed about the dualcore.
 16. The golf ball of claim 15, wherein the fatty acid amide is aprimary monoamide selected from the group consisting of stearamide,oleamide, erucamide, behenamide, and palmitamide, and mixtures thereof.17. The golf ball of claim 16, wherein the primary monoamide is asubstituted monoamide selected from the group consisting of lauryloleamide, stearyl erucamide, hydroxy fatty acid amides, N-methylol fattyacid amides, and cocamide diethanolamide, and mixtures thereof.
 18. Thegolf ball of claim 15, wherein the fatty acid amide is a bisamideselected from the group consisting of ethylene bis(stearamide),methylene bis(oleamide), and mixtures thereof.
 19. The golf ball ofclaim 15, wherein the polyamide composition has a flex modulus of 20,000psi to 150,000 psi and the rubber composition has a flex modulus of1,000 to 60,000 psi, the flex modulus of the polyamide composition beinggreater than the flex modulus of the rubber composition.
 20. The golfball of claim 15, wherein the center hardness of the inner core is about50 Shore D or greater and the surface hardness of the outer core isabout 15 Shore D or greater, the center hardness of the inner core beinggreater than the surface hardness of the outer core layer.